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kirkt

[AP] Film Emulation looks using Inferred LUTs in AP

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Hi folks,

 

There are several different ways to achieve looks in your image editing workflow, and one of them that can be useful is the LUT (Look Up Table).  Affinity Photo has an adjustment layer called "LUT" which permits the user to include a LUT in their layer stack, giving non-destructive control to the image look, etc. through a color LUT.

 

The typical use of the LUT adjustment layer is to load a pre-made LUT (in various forms, like .cube, etc.) and season to taste.  The AP LUT adjustment layer also provides an interesting second method, the "Infer LUT" mode.

 

As the name suggests, the Infer LUT mode asks the user to load two images: the first image is sometimes referred to as the "Identity" image - the non-modified reference image; the second image is the modified image, typically the Identity image put through some sort of processing to get the final, transformed look.

 

One handy tool for storing inferred LUTs is the HALD LUT identify image - here is a brief explanation of the HALD:

 

http://www.quelsolaar.com/technology/clut.html

 

It is essentially a compact image composed of color patterns that can be visualized as a 3D color matrix.  It is usually stored in a non-lossy file format, like PNG.  When you apply edits to the identity HALD image, the colors in the image change accordingly, and the edits are "recorded."  When you compare the original Identity HALD image to the edited HALD image, the transforms in color can be inferred and, voila, you have a LUT!  It is efficient and compact, so you can get good resolution of the LUT transform in a small package.

 

AP can use the HALD identity image and a transformed version of that image to infer a LUT.  Why is this cool?  Because you can use any piece of software you would like, create a look you want on a working image (any image) - once you have the look you want, you insert the HALD image into the workflow and apply the exact same transform and save the resulting, edited HALD image.  You can build a library of the Identity HALD and then all of your edited HALD images and load the Identity and the Edited HALD image that has the look you want to apply into the AP LUT adjustment layer and POW! You can apply your look via the Infer LUT mode.

 

This is a nifty way to export all of your presets from something like Lightroom, where you paid $$$ for the VSCO film pack presets, for example, into a useable HALD LUT.

 

Because it's fun, I've included a link here:

 

http://blog.patdavid.net/2015/03/film-emulation-in-rawtherapee.html

 

That describes film emulation looks using this same technique, along with a bunch of freely downloadable HALD LUTs for those films.  The context is within the film emulation module of Raw Therapee, but the functionality is identical to AP's Infer LUT.

 

When you download the film emulation HALDs from the above link, read the README.txt file for more details.  The collection includes the identity HALD and a bunch of HALDs that capture various film looks.  The looks are all made in 8bit sRGB, but no one is going to analyze your look transform if you use it in a 16 bit document or a slightly larger color space, so have at it!

 

Remember, you can do this with any look you create, in any application, as long as you can repeat the procedure (for pixel-based operations) or insert the identity HALD into your non-destructive layer stack.

 

Also, LUTs do not capture non-tonal/color operations like chromatic aberration correction, etc.  Also, with respect to film emulation, this is for tonal edits and does not emulate grain.

 

Have fun!  This is a great feature to have in AP, but maybe not as celebrated as it could be!

 

kirk

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I sort of figured this was covered before, but a search for LUT and Infer LUT came back with nothing.  Sorry about that.  Thanks for the tip!

 

kirk

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I was wondering if this could be added to Affinity - thanks for the information. I'm storing the Inferred LUTs as Presets. Can any tell me where the LUT Preset files are stored (on a Mac)?

 

Cheers,  :)

Biff 

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